In the text below, the two terms magnetic resonance imaging system and magnetic resonance imaging scanner are used synonymously.
Magnetic resonance imaging scanners simultaneously receive a multiplicity of magnetic resonance signals via local antennas that are applied to the patient and that are part of a number of local coils. The analog magnetic resonance signals received in the process are supplied, particularly following preamplification, to a reception system, processed further therein on an analog basis, digitized and forwarded to an image reconstruction unit as raw data in order to reconstruct image data.
A fundamental problem in this case is that local coils from a more recent generation are incompatible with the reception systems of MRIs from an earlier generation, and also vice versa.
The patent specification DE 10 2008 023 467 B4 describes an arrangement for transmitting magnetic resonance signals in which the individual received signals from the local antennas of the local coils are first of all converted in pairs into dedicated intermediate frequency bands and are then transmitted in pairs using a 2:1 frequency division multiplex method (FDM) via a common line. In this case, the two intermediate frequency bands are arranged mirror-symmetrically with respect to a sampling rate of a downstream analog/digital conversion section. As a result, the two bands appear at the same position in baseband following sampling. By way of example, in the case of local coils from a more recent generation (TiM4G 1.5 T systems), the received signal is converted from 63.6 MHz with local oscillator signals at frequencies of 55 MHz and 75 MHz to intermediate frequency bands around 8.6 MHz and 11.4 MHz. The bandwidth of the received signal may be up to ±500 kHz in this case. Following spectral separation and subsequent sampling at 10 MS/s in each case, both signals appear at a second (e.g., digital) intermediate frequency of 1.4 MHz in the correct position in each case. By way of example, the reception paths of the TiM4G systems are based on the architecture depicted in FIGS. 3 and 4 in the patent specification DE 10 2008 023 467 B4. The resulting 1.4 MHz baseband signals are transferred to the digital signal processing section at a data rate of 10 MS/s.
The “TiM LC interface” carries a respective MR received signal per coaxial connector at the RF level (e.g., 63.6 MHz in the case of 1.5 T systems), while the “TiM4G-LC interface” carries two MR signals per coaxial connector using frequency division multiplexing at an intermediate frequency level (e.g., 8.6 MHz and 11.4 MHz in the case of 1.5 T systems; in this regard see the patent specification DE 102008023467 B4).
Further properties of “TiM local coils” from an earlier generation and “TiM4G local coils” from a more recent generation include the following.
TiM refers to local coil signal transmission at the MR frequency (RF transmission), and 8 local coil signals per local coil connector.
TiM4G refers to frequency conversion of the local coil signal within the local coil and local coil signal transmission at two intermediate frequencies (e.g., 2:1 frequency division multiplexing symmetrically with respect to 10 MHz; such as at 8.6 MHz and 11.4 MHz, which is to say 10 MHz+−1.4 MHz, in the case of 1.5 T), and 24 local coil signals per local coil connector.